IEEE Computer Volume 15 Number 6 -- THE OPEN CHANNEL
Original Publication Date: 1982-Jun-01
Included in the Prior Art Database: 2005-Nov-11
Software Patent Institute
Charles McCabe: AUTHOR [+3]
THE OPEN CHANNEL
THIS DOCUMENT IS AN APPROXIMATE REPRESENTATION OF THE ORIGINAL.
This record contains textual material that is copyright ©; 1982 by the Institute of Electrical and Electronics Engineers, Inc. All rights reserved. Contact the IEEE Computer Society http://www.computer.org/ (714-821-8380) for copies of the complete work that was the source of this textual material and for all use beyond that as a record from the SPI Database.
THE OPEN CHANNEL
San Francisco Chronicle
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A scatological tutorial on terminal protocols
With all of the action in local networking now taking place, not much attention is being paid to Terminal Protocols (TP), which are much simpler in concept. The United States has raised TP to a very high level, while other countries, particularly Great Britain, have lagged in TP technology.
Just what is involved in TP? The atomic level of TP, as with most computer technology, is based on the bit. However, just a bit of TP is not very useful. Bits are blocked into "sheets" much like frames in data-link protocols. Each sheet is separated from adjacent sheets by flag-type characters called "perfs." A complete message may require several sheets forming a TP "roll." Finally, a session may require several rolls, thus making a "carton" of TP.
Although more complex protocols have seven layers, TPs have only one or two, called "plys." A two-ply TP consists of a physical or "bottom" layer and a logical or "top" layer. One-ply TP has only a physical layer. Generally, twoplyTP is considered superior to the oneply variety.
Both token-passing and CSMA techniques are allowed in TP. The TP token is called a Generally Asynchronous Symbol (GAS) and in most TP systems is represented by the ASCII character CAN (decimal 24). Thus, token passing is called "passing GAS." It is permissible in TP to hold on to the token for a while if a message is almost ready for transmission. However, some manufacturers have abused this rule, designing products that hold the token far too long. This leads to situations where there is far too much "sitting on the CAN."
The medium used to transmit TP is generically called a "pipe." a term stolen horn the Bell Laboratories' Unix system. The installation of a TP system is usually referred to as "installing the plumbing." One of the great advantages of TP over the more complex local network protocols is
IEEE Computer Society, Jun 01, 1982 Page 1 IEEE C...